How to manage a hyponatremic (low serum sodium) adult patient with a serum sodium level of 130 mmol/L?

Management of Serum Sodium 130 mmol/L

For a patient with serum sodium of 130 mmol/L, begin with a thorough assessment of volume status and symptom severity, as this level warrants investigation and potential treatment depending on clinical context. 1

Initial Assessment

Determine volume status through physical examination:

• Look for hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Look for hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1
• Euvolemic patients show none of these findings 1

Obtain essential laboratory tests:

• Serum and urine osmolality 1
• Urine sodium concentration 1
• Urine electrolytes 1
• Serum uric acid (levels <4 mg/dL suggest SIADH with 73-100% positive predictive value) 1
• Thyroid function tests to exclude hypothyroidism 1
• Assess for medications causing hyponatremia 2, 3

Treatment Based on Symptom Severity

Asymptomatic or Mild Symptoms

At sodium 130 mmol/L without severe symptoms, treatment focuses on the underlying cause rather than emergent correction. 1

• Monitor serum sodium every 24-48 hours initially 1
• Avoid rapid correction as this level does not require emergency intervention 2
• Even mild hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and mortality 1, 2

Severe Symptoms (Seizures, Coma, Altered Mental Status)

If severe symptoms develop, administer 3% hypertonic saline immediately with target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1, 2

• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Check serum sodium every 2 hours during active correction 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion. 1

• Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 1
• Discontinue diuretics immediately 1
• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1

Euvolemic Hyponatremia (SIADH)

Implement fluid restriction to 1 L/day as first-line treatment. 1, 2

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• Consider vasopressin receptor antagonists (tolvaptan 15 mg once daily) for resistant cases 1, 2
• Alternative options include urea, demeclocycline, or lithium 1, 2

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day. 1, 3

• Temporarily discontinue diuretics if sodium drops below 125 mmol/L 1
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Sodium restriction (not fluid restriction) results in weight loss as fluid follows sodium 1

Critical Correction Rate Guidelines

Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1, 2

• Standard correction rate: 4-8 mmol/L per day 1
• For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): limit to 4-6 mmol/L per day 1, 4
• If overcorrection occurs, immediately switch to D5W and consider desmopressin 1

Special Populations

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments. 1

• SIADH: euvolemic, treat with fluid restriction 1
• CSW: hypovolemic with CVP <6 cm H₂O, treat with volume and sodium replacement, never fluid restriction 1
• In subarachnoid hemorrhage patients at risk for vasospasm, avoid fluid restriction 1
• Consider fludrocortisone 0.1-0.2 mg daily for CSW 1

Cirrhotic Patients

Hyponatremia at 130 mmol/L in cirrhosis increases risk of complications. 1

• Increased risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Require more cautious correction (4-6 mmol/L per day maximum) 1
• Fluid restriction may prevent further decline but rarely improves sodium significantly 1

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L) as clinically insignificant - it increases mortality and fall risk 1, 2
• Never use fluid restriction in cerebral salt wasting - this worsens outcomes 1
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours - this causes osmotic demyelination syndrome 1, 4
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms - it worsens fluid overload 1
• Never fail to assess volume status accurately - physical examination alone has poor sensitivity (41.1%) and specificity (80%) 1